Influence of TBM cutter configurations on gravel excavation characteristics revealed by discrete element method

Over the past few decades, as urbanization has progressed, the demand for infrastructure has increased. The shield tunnelling method has been widely applied for underground space development, particularly in urban areas. The tunnel boring machine (TBM) contacts with the geological strata through a process of propelling and rotating. The complex excavation process often leads to severe wear on the cutting tools of the TBM cutterhead, especially in gravel layer, increasing construction costs and project durations significantly. This study establishes a methodology to investigate the influence of cutter configurations on gravel excavation characteristics and to evaluate the cutter wear during tunnel excavation. Numerical simulation using the discrete element method, PFC3D is conducted to mimic the irregular shape and particle size distribution of gravel and their impact on gravel excavation. The effects of different opening ratios, type of cutting tools, and height of cutting tool of the cutterhead on gravel excavation, as well as the mechanism of cutting tool breaking through gravel layer are also examined. The simulation results indicate that cutter bits exhibit a peeling cutting mode, while disc cutters adopt cutting and fragmentation. Simultaneously employing both types of cutting tools on the cutterhead can enhance tunnel excavation efficiency. The method for simulating cutter wear on gravel developed in this paper can provide insights for the analysis and design of shield cutterheads in gravel layer.